(1) Field of the Invention
This invention relates to a process for production of ionic metal-containing cured rubbers (i.e., metal-containing cured rubbers which have ionic bonds in their molecules). More particularly, it relates to a process for producing the ionic cured rubbers which comprises reacting a liquid rubber having terminal carboxyl groups which have been partially neutralized with metal ions with a bisepoxide and a dibasic acid anhydride. The invention can be advantageously applied to the industrial fields where conventional liquid rubbers have been cured into solid elastomers.
(2) Description of the Prior Art
Heretofore, introduction of ionic bonds into rubber polymers has been carried out by preparing first a rubber having functional groups capable of forming ionic bond, such as carboxyl groups, and then neutralizing the rubber with metal ions. This method, however, has difficulty in that the neutralization reaction does not sufficiently proceed and the unreacted metal ion-forming agent is difficult to be removed. Presence of the unreacted metal ion-forming agent may often result in opaqueness of resulting rubber. Further, the neutralization reaction produces undesirable by-products such as water. Particularly, it is very difficult, according to this method, to effectively introduce ionic bonds into three-dimensional polymers.
The liquid rubbers to be used such as carboxyl-terminated polybutadienes and carboxyl-terminated butadiene-acrylonitrile copolymers are commercially available from the B. F. Goodrich Company, U.S.A. and sold under trade name "Hycar". The main uses of these liquid rubbers have been for sealants, moisture-resistant compounds, binders for rocket- or missile-propellents, encapsulation or potting in electric industry and the like.
The present inventor has paid attention to the fact that the liquid rubbers aforementioned have carboxyl groups at their both terminal positions, and has found that the rubber can be partially neutralized by adding thereto a polyvalent metal ion-forming agent. Furthermore, the present inventor has found that by adding, to the liquid rubber thus partially neutralized, a bisepoxide and a dibasic acid anhydride and then heating the resulting mixture, reaction proceeds in the absence of a catalyst to produce a metal-containing ionic cured rubber in one step. Thus, the present invention has been accomplished.
The object of the invention is to provide a process for producing a novel metal-containing ionic cured rubber from the above-mentioned liquid rubber in one step without using any catalyst.
Other objects of the invention will be made clear in the following description.